1. Technical Field
The present invention relates generally to carrier phase recovery, and more particularly, to modulation-independent feed-forward carrier phase recovery with a multiplier free structure.
2. Description of the Related Art
Carrier phase recovery is an important problem in optical coherent detection schemes, because of the phase noise incurred from laser linewidth. As use of multimedia communications services over packet data networks (e.g., the Internet) continues to grow, the demand for higher capacity in core data transport networks also continues to grow. Core data networks may include optical networks based on fiber optic technology. To increase the capacity of optical networks, advanced signal modulation techniques, such as quadrature phase shift key (QPSK) and quadrature amplitude modulation (QAM) have been developed. In particular, M-ary QAM (M-QAM) (e.g., 16-QAM and 64-QAM) have the potential to realize high-speed optical transmission with high spectral efficiency.
Digital coherent detection has been employed for detecting and demodulating received optical signals, and a key step in digital coherent detection is carrier phase recovery. Carrier phase may be degraded by laser phase noise in a received optical signal, and laser phase noise is dependent on the linewidth of the optical carrier. For example, for high-order M-QAM modulation formats (e.g., M>4), the tolerance for laser phase noise becomes smaller as the modulation increases. As modulation formats become higher and higher, there is a need for a carrier phase recovery system and method to be universal to any modulation format (e.g., modulation independent characteristics).
Various carrier phase recovery systems and methods have been developed, but there are very few systems and methods available that are capable of performing modulation-independent carrier phase recovery. For example, one existing modulation-independent carrier phase recovery system employs a feedback structure with a cost function to remove the dependence on modulation formats. However, the cost function is not sensitive to phase errors, and requires feedback to adjust the phase estimation, which is not practical for use in a parallel architecture. Moreover, none of the existing systems and methods are capable of performing multiplier-free carrier phase recovery.